Orbivan

CLINICAL PHARMACOLOGY

This combination drug product is intended as a treatment for tension headache.

It consists of a fixed combination of butalbital, acetaminophen, and caffeine. The role each component plays in the relief of the complex of symptoms known as tension headache is incompletely understood.

Pharmacokinetics

The behavior of the individual components is described below.

Butalbital

Butalbital is well absorbed from the gastrointestinal tract and is expected to distribute to most tissues in the body. Barbiturates in general may appear in breast milk and readily cross the placental barrier. They are bound to plasma and tissue proteins to a varying degree and binding increases directly as a function of lipid solubility.

Elimination of butalbital is primarily via the kidney (59% to 88% of the dose) as unchanged drug or metabolites. The plasma half-life is about 35 hours. Urinary excretion products include parent drug (about 3.6% of the dose), 5-isobutyl-5-(2, 3-dihydroxypropyl) barbituric acid (about 24% of the dose), 5-allyl-5(3-hydroxy-2-methyl-l-propyl) barbituric acid (about 4.8% of the dose), products with the barbituric acid ring hydrolyzed with excretion of urea (about 14% of the dose), as well as unidentified materials. Of the material excreted in the urine, 32% is conjugated.

The in vitro plasma protein binding of butalbital is 45% over the concentration
range of 0.5-20 mcg/mL. This falls within the range of plasma protein binding
(20%-45%) reported with other barbiturates such as phenobarbital, pentobarbital,
and secobarbital sodium. The plasma-to-blood concentration ratio was almost
unity, indicating that there is no preferential distribution of butalbital into
either plasma or blood cells. See OVERDOSAGE for toxicity information.

Acetaminophen

Acetaminophen is rapidly absorbed from the gastrointestinal tract and is distributed
throughout most body tissues. The plasma half-life is 1.25 to 3 hours, but may
be increased by liver damage and following overdosage. Elimination of acetaminophen
is principally by liver metabolism (conjugation) and subsequent renal excretion
of metabolites. Approximately 85% of an oral dose appears in the urine within
24 hours of administration, most as the glucuronide conjugate, with small amounts
of other conjugates and unchanged drug. See OVERDOSAGE for toxicity information.

Caffeine

Like most xanthines, caffeine is rapidly absorbed and distributed in all body tissues and fluids, including the CNS, fetal tissues, and breast milk.

Caffeine is cleared through metabolism and excretion in the urine. The plasma
half-life is about 3 hours. Hepatic biotransformation prior to excretion results
in about equal amounts of 1-methylxanthine and 1-methyluric acid. Of the 70%
of the dose that is recovered in the urine, only 3% is unchanged drug. See OVERDOSAGE
for toxicity information.

Last reviewed on RxList: 8/15/2011
This monograph has been modified to include the generic and brand name in many instances.